The present invention relates to the field of ink jet inks, and more particularly to the field of ink jet inks which have been formulated for use in drop on demand ink jet printers.
Drop on demand ink jet printers present a number of unique problems which are not encountered by many other types of ink jet printers. For example, drop on demand ink jet printers may have to sit in a stand-by or cooled down mode for some period of time between printing cycles. Unlike continuous stream ink jet printers, which will "clean out" the ink which has been standing in the discharge orifice, drop on demand printers normally operate by beginning the printing cycle with such material. Accordingly, start-up problems are often encountered if the subject inks are not specially formulated to reduce such start-up problems. See for example, U.S. Pat. No. 4,400,215, relating to methods and inks for reducing start-up problems.
IR readable inks are also known. See European application EP-147257-A published July 3, 1985 assigned to Eastman Kodak, disclosing IR readable bar code ink jet inks comprising a dye, binder, solvent blend and specific IR absorbing compound. Another example of an IR readable ink used in a different context is disclosed in U.S. Pat. No. 4,069,179 (Jones) which discloses transfer elements comprising a substantially non-absorbent base having a coating comprising a continuous phase containing, as a discontinuous phase, a colorant carried by a vehicle comprising at least one C.sub.12 to C.sub.20 alcohol, said vehicle having a melting point below about 20.degree. C. A variety of colorants, including salts of dyes and pigments such as carbon black, and/or a nigrosine base colorant admixed with a fatty acid developer such as oleic acid are disclosed.
Other beneficial characteristics of drop on demand inks include the obtainable dot size and clarity of print generated by drop on demand printers. This problem is addressed in U.S. Pat. No. 4,361,843, which discloses that suitable drop on demand ink jet inks may comprise a mixture of oleic acid in an approximate weight of from 20 to 80 percent of the total mixture of the composition. The therein disclosed ink also includes a dye or a dye in a solvent. In this regard, also refer to Japanese patent application 017,758, filed Feb. 22, 1977 to Toyo, Inc. Mfg.; and Japanese patent application 132,548, filed Nov. 28, 1973 entitled "Ink Compositions for Ink Injection Type Recording Apparatus".
Various additives have been suggested for use with inks comprising oleic acid. See for example the above-mentioned U.S. patent, which discloses, inter alia the use of a solvent comprising benzyl alcohol and/or benzyl ether. Of course, these inks also disclose various colorants, including dyes such as typophor black, chinoline yellow, oil yellow, and nigrosine base. In this regard, it should be noted that typophor black as commonly provided comprises 30 weight percent of nigrosine and 70 weight percent of oleic acid. In U.S. Pat. No. 4,386,961, additional ink jet ink compositions are disclosed which comprise small proportions of oleic acid, and relatively larger proportions of benzyl alcohol and propylene glycol. Alternatively, formulations up to 10 percent oleic acid combined with diethylene glycol and methoxy triglycol together with a colorant and one or more additives are also disclosed in this U.S. patent.
Another approach which has been taken is the formulation of ink jet inks which are solid at room temperature. These include those described in U.S. Pat. No. 4,390,369 in related application Ser. No. 644,542, filed Aug. 27, 1984, entitled "High Molecular Weight, Hot Melt Impulse Ink Jet Ink", and, to the extent applicable, those ink compositions cited in connection with the prosecution of that patent and its related applications. For example, the Kurz and Berry patents, which relate to electrostatic printing processes, disclose the use of various inks including inks comprising didodecyl sebacate.
For further disclosures of ink jet inks, also please refer to U.S. patent application No. 565,124, filed Dec. 23, 1983, entitled "Stearic Acid Containing Ink Jet Inks", and its parent application Ser. No. 394,154, filed July 1, 1982. Also of interest is application Ser. No. 672,587, filed Nov. 16, 1984, entitled "Low Corrosion Impulse Ink Jet Ink", which discloses an ink jet ink comprising a fatty acid vehicle, a colorant, and amounts of anti-oxidant which are effective to substantially reduce the rate of ink induced metal corrosion. In accordance with this disclosure, the preferred fatty acid vehicle is oleic acid, which is described as comprising 10 to 97 weight percent of the subject ink. The subject ink further comprises 10 to 90 weight percent of a vehicle additive which may, for example, comprise benzylalcohol, benzyl ether or any of a variety of other specified additives. The subject application further discloses that the preferred inks comprise 3-20, preferably 10-17, more preferably 15 weight percent of one or more vehicle-soluble dyes, such as chinoline yellow, nigrosine base, acetosol brown, orasol black, and oil yellow.
Notwithstanding the advances and disclosures represented in the aforementioned patents and patent applications, a need still exists for a liquid ink jet ink which is readily jettable by drop on demand ink jet printers, which is not susceptible to start-up problems after extended periods of printer inactivity, which produces a high print quality, and which otherwise exhibits beneficial ink jet ink characteristics.